A tape drive device is to write data output from a host machine to a magnetic tape to record and store the data. A well-known tape drive device has buffer memory to smoothly communicate data with the host machine.
The data output from the host machine is temporarily accumulated in the buffer memory of the tape drive device, and then written to the magnetic tape. The writing process is performed when the amount of data accumulation in the buffer memory reaches a specified value (for example, 70% of the memory capacity), or when a specified instruction (for example a write file mark instruction, a rewind instruction, an unload instruction, etc.) is received from the host machine.
The write file mark instruction is to write the data as a mark indicating the end of a data file to the magnetic tape. The rewind instruction is to rewind the magnetic tape. The unload instruction is to eject a cartridge tape from the tape drive device.
Since the buffer memory provided for the tape drive device is used as described above, volatile memory which has a high free level of access and is accessed at a high speed is generally used as the buffer memory.
The magnetic tape device is a storage device which has been long used in the history of a computer system for a batch job mainly under the control of the mainframe machine. The magnetic tape device is recently used for a high-speed backup of a large volume of data under the control of various open systems.
In the wide use of the device, a batch job uses a small block size of data and a small file size. Therefore, reading and writing operations of data are frequently performed to a magnetic tape. Accordingly, the capacity of the buffer memory of the device is small, for example, 32 kilobytes, and the activating and stopping time in operating a magnetic tape when the position of the magnetic tape is performed in a short time with high accuracy is, for example, several ten milliseconds. In addition, the data transfer function among the host machines of devices is 20 megabytes/second sufficiently. Furthermore, the magnetic tape medium used in this application has been changed from an open reel device to a cartridge device. The recording capacity of the magnetic tape medium ranges from 200 megabytes to 800 megabytes (when data is not compressed), and the length of the magnetic tape is about 335 m (thickness of the tape is about 27 micrometers).
Data has been recorded on the magnetic tape in one way of 9 through 18 data tracks in the tape width direction at the early stage of the cartridge device, and in both ways of 18 data tracks (a total of 36 data tracks) at the later stage of the device.
On the other hand, the magnetic tape device in the LTO (linear tape open) specification which is the dominant device in a backup application is appropriate for backup of a large volume of data of large block size and file size.
The recording capacity of the cartridge in the magnetic tape device ranges from 100 gigabytes (when data is not compressed) in the first generation to 1500 gigabytes (when data is not compressed) in the latest fifth generation. On the other hand, since the shape of the cartridge is not largely different from that in the batch job period, the magnetic tape becomes longer and thinner, and is 846 meter long and 6 micrometer thick.
In recording data on the magnetic tape in the LTO specification in the fifth generation, data is written to a total of 1280 data tracks by moving 40 times back and forth on 16 data tracks. The transfer function with the host machine is performed at a high speed of 140 megabytes/second in the fifth generation. Thus, since a large volume of data is processed, the desired buffer memory is as large as 256 megabytes.
The specification of the magnetic tape device is prepared to avoid as much as possible the activating and stopping operations on the magnetic tape on which a large volume of data is read and written with the physical restriction of the thickness of the magnetic tape, and the speed used to activate and stop the tape is as low as 3 or 4 seconds.
With a larger capacity of the magnetic tape recording device, the production information, the specification information, the quality information, etc. about the magnetic tape are to be recorded and updated on the magnetic tape. In the LTO specification, the tape cartridge which sores a magnetic tape is designed to include a noncontact and non-volatile memory device, and various types of management information are recorded and updated in the memory.
Another background technique is to include non-volatile memory in the tape cartridge which stores a magnetic tape, and store in the memory the management information about the recorded contents of the data on the magnetic tape.
There are the techniques described in the following documents.    Document 1: Japanese Laid-open Patent Publication No. 2003-123342    Document 2: Japanese Laid-open Patent Publication No. H11-316987    Document 3: Japanese Laid-open Patent Publication No. S60-32177
The tape drive device reads and writes data in the period in which the magnetic tape is stably driven at a constant speed. Although the drive of the magnetic tape is to be stopped after completing the write of data, the magnetic tape is not stopped immediately. Therefore, the position of the magnetic head for recording data on the magnetic tape is apart from the position of the completion of the write of the data when the drive of the magnetic tape is completely stopped. Therefore, if the next data is to be written on the magnetic tape without space from the completion position of the write, the rewinding operation of the magnetic tape is performed to some extent, and then the driving operation is resumes in the direction of the write. Then, after driving the magnetic tape at a constant speed, it is preferable to write the next data when the write completion position passes the position of the magnetic head while recognizing the data block number recorded on the magnetic tape and the position information on the magnetic tape.
As described above, the tape drive in the LTO specification is good at writing and reading data of a large block size and a large file size at a high transfer speed.
However, the magnetic tape recording device operates at instructions on a data block size, a file size, etc. output from the host machine. For example, assume that the data transfer speed is low on the host machine, for example, when data of small block size and a small file size is transmitted to the tape drive in the LTO specification, when data is discontinuously transmitted from the host machine, etc. In this case, since sometime is used to reach a specified capacity of buffer memory, the tape drive temporarily stops the operation of the tape, and when the specified capacity of the buffer memory is reached, the operation of writing data on the magnetic tape is resumed. Therefore, the processes of grasping the write completion position, and activating and stopping time of the magnetic tape are used for the tape drive. In addition, when an instruction as a trigger of writing data on the magnetic tape is transmitted each time a small volume of data is accumulated on the buffer memory, the tape drive frequently activates and stops the magnetic tape, thereby degrading the data transfer function of the tape drive.
The tape drive in the LTO specification has the system of suppressing the excessive reduction of the data transfer function between the host machine and the drive by reducing the activating and stopping operations of the magnetic tape by setting a lower writing speed on the magnetic tape when the data transfer speed on the host machine side is slow. The system is referred to as a speed matching function etc. by some drive manufacturers.
The function effectively works on the 30% through 40% of the maximum transfer function of the tape drive in the LTO specification. However, in using the above-mentioned batch job, a low transfer speed exceeding the corresponding range of the speed matching function is used. Therefore, the function in the LTO specification does not fully work.
On the other hand, the magnetic tape recording device for enterprises having a specification similar to the LTO specification may have the function referred to as a skip-sink function etc. as a function intended for a batch job use under control of the mainframe. The function makes the speed of the transfer function of the tape drive viewed from the host machine look faster by discontinuously writing data on the magnetic tape without stopping the tape operation when the data transmitted from the host machine is written on the tape. Then, the data is rewritten for continuity by reading again the data discontinuously written on the magnetic tape by the tape drive.
However, in this function, if there is a partially damaged or stained portion in the rewrite position when the data is rewritten, the data rewriting process may fail and the data may be lost.